What I meant was that you have verbal permission from the photographer to use the images in exchange for photo props, but hadn't realised that everyone gets written consent as well. Of course it's illegal to use images without permission, I'm well aware of that.. the reason I watermark every single one of my images.

If you are dealing with the photographer directly, verbal permission is ok as long as you aren't dealing with someone who's out to cause trouble... I would suggest written permission if you use a model who's photographer is not direct relation such as the mother / father of the child...